The encouraging results of the neutron radiotherapy trials at Hammersmith (London) have been recognized for some time. Trials are now beginning in America, two at considerably higher neutron energies than used at Hammersmith where the average energy is approximately 6 MeV. Evidence also exists from radiobiology studies that, compared to photons, neutrons produce more consistent lethal changes in cells and are less sensitive to effects such as cell cycle and hypoxic conditions. Tissue-equivalent (TE) ionization chambers, used by radio-therapists to measure the dose are not completely TE, and they provide no information concerning the microscopic distribution of absorbed energy which relates more directly to biological effectiveness. To correct for the lack of tissue equivalence and obtain microscopic information one needs to know the charged particle angular and energy spectra for the tissue resident (TR) elements at each neutron energy in the therapy beam. A serious problem exists in that above 14 MeV very little is known about charged particle production cross sections for tissue-resident elements with respect to particle type, number, angular and energy distribution of the particles produced. We propose to measure these cross sections for tissue resident elements C, N, and O using a neutron beam of good energy resolution. The advantage of using good energy resolution (delta E approximately minus 1 MeV) at 5 - 10 MeV intervals is that theoretical models can be used to calculate the kerma, dose and LET spectrum for any neutron spectrum, so that corrections can be applied to allow high precision dosimetry for the neutron spectra now being used in therapy. In addition a better understanding of dose and LET measurements will be achieved. These calculations will be made mainly by a theoretical group at Naval Research Laboratory with some being done at University of California, Davis.